A Quadrant is the fourth part of a Circle, containing 90 degrees, and representeth the distance between the Horizon & Zenith, being an excellent Instrument upon the Shore to perform any Astronomical Observations, but for a Seaman it is to no purpose: & although there may be very much written of the commodious and excellent uses of the Quadrant, yet not being an apt Instrument for Sea-observations, it shall be from my purpose to write further thereof, and therefore the only laying down of this form, may at this present suffice

There hath been great pains taken to many for the enlarging of the degrees contained in an Astrolabe, among which there is a Projection to convey the degrees of a Quadrant into the concavity of an Astrolaby whereby the degrees shall be double to any other Astrolaby of the same quantity, so that the Sun-beam, piercing a hole made in the side of the Astrolaby is thereby carried to the degrees noted in the opposite concave part, as by this Form may appear.

Also myself laboring in the same matter, have found a means whereby an Ark of a Quadrant, whose side is 10 foot, may be convered into an Astrolaby of 10 inches diameter, whode Dioptra shall cut his limb to right angles, and shall perform the complement of 90 degrees, as simple and as effectually as by the Quadrant it may in any sort be done. Whose demonstration, together with the demonstration of my Staff, I purpose (God willing) at large to manifest:

But there can be no Invention that can establish the certainty of the use of either Quadrant or Astrolaby at Sea, for unless it be very smooth water, there can be no certainty of any observation by those Instruments, whereby the Seaman may rest assured of the Altitude which he seeketh but the Observations made by the Cross-staff are without all distruct of error, and therefore no Instrument may compare with the excellence of this Cross-staff for the Seamans use.

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F I N I S.

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